Workshop on SMART Cable Applications in Earthquake and Tsunami Science and Early Warning; Potsdam, Germany, 3 4 November 2016 Short Report

Transcription

1 Workshop on SMART Cable Applications in Earthquake and Tsunami Science and Early Warning; Potsdam, Germany, 3 4 November 2016 Short Report Frederik Tilmann + Bruce Howe, Rhett Butler, Stuart Weinstein SMART cable workshop Brest November 13 Supported by: Tilmann SMART cables / Earthquakes and tsuname application 1 / 9

2 Application: Tsunami early warning Pacific ring of fire warning times with hypothetical cable routes (S. Weinstein) Trivially, increased number of sensor make it easier to characterise tsunami Trench-parallel cables would have even larger impact. Tilmann SMART cables / Earthquakes and tsuname application 2 / 9

3 Application: Tsunami early warning Simulated earthquake in Gulf of Cadiz (M. Nosov, A. Babeyko) Virtual DART position for optimal warning times Sea surface evolution at 60 s after nucleation Tilmann SMART cables / Earthquakes and tsuname application 3 / 9

4 Application: Tsunami early warning Simulated earthquake in Gulf of Cadiz (M. Nosov, A. Babeyko) Simulated bottom pressure under Buoy 1 For comparison: actual data from Tohoku earthquake Four regimes dominate depending on freq f and H, depth of seafloor (m): Acoustic waves f > c/4h T < 13 s for H=5000 m Forced oscillations c/4h > f > 0.37 g/h 13 s< T <61 s Dispersive gravity waves 0.37 g/h > f > g/h 61 s< T < 314 s Long gravity waves f < g/h T > 314 s (c. 5 min) Tilmann SMART cables / Earthquakes and tsuname application 4 / 9

5 Global tomography Assuming ray theory (C. Rowe and N. Ranasinghe) Station and seismicity distribution: Assumed cable sites: Coverage below the oceans markedly improved even into the lower mantle. Tilmann SMART cables / Earthquakes and tsuname application 5/9

6 Other applications Earthquake early warning (EW) Earthquake source modelling for tsunami EW and earthquake physics Local earthquake studies Surface wave / ambient noise Local structure: Monitoring near-sensor elastic properties Local structure: Compliance Seafloor geodesy: vertical motion of the seafloor from pressure Tilmann SMART cables / Earthquakes and tsuname application 6 / 9

7 Review of proposed instrumentation Accelerometers and pressure sensors Acceleration 10 log10 (m/s 2 ) in 1/3 octave band Mw7.5 Mw6.5 Mw5.5 Surface waves W phase P wave arrival Mw6.5 Mw5.5 Mw7.5 Noise North Atlantic (BB) SMART cable spec W Phase Surface waves Microseisms, Body waves SMART cable spec Microearthquakes Freq (Hz) Current spec acceleration: PSD (2 ng) 2 /Hz=-154 db (m 2 /s 2 /Hz) for frequencies Hz Current spec acceleration: -8 db (Pa 2 /Hz) at <10 Hz But: many applications in seismology require longer period response Pressure can be used for these as well, but acc+pressure allows to improve signal/noise ratio by removing infragravity wave influence at long periods Recommendation: extend sensitivity range of accelerometers to longer periods Tilmann SMART cables / Earthquakes and tsuname application 7 / 9

8 Recommendations Applications: SMART cables can significantly cut down early warning delays for tsunami early warning and improve the accuracy of forecast. A tangible improvement can also be achieved for earthquake early warning. Cable routes parallel to major subduction trenches would be of most interest to tsunami and large earthquake researchers. 50 km sensor spacing in the deep ocean would be (marginally) enough to sample details of the tsunami wavefield, allowing analysis of source and propagation effects even for non-seismic sources, such as landslides. Instrumentation: Scientific uses in global tomography and tectonics (local earthquake studies) would benefit strongly from high-sensitivity accelerometers operating at longer periods, beyond the current specifications. Long term stability of pressure sensors is of no concern for early warning applications, but is needed for geodetic applications Wet demonstrator Wet demonstrator should already return science data in addition to proving concept. In Europe a suitable location could be in Greece due to subduction related high seismicity but no large-scale cabled observatory in place. In North America Ocean Network Canada and Ocean Observatories Initiative have expressed willingness Tilmann SMART cables / Earthquakes and tsuname application 8 / 9

9 Recommendations Applications: SMART cables can significantly cut down early warning delays for tsunami early warning and improve the accuracy of forecast. A tangible improvement can also be achieved for earthquake early warning. Cable routes parallel to major subduction trenches would be of most interest to tsunami and large earthquake researchers. 50 km sensor spacing in the deep ocean would be (marginally) enough to sample details of the tsunami wavefield, allowing analysis of source and propagation effects even for non-seismic sources, such as landslides. Instrumentation: Scientific uses in global tomography and tectonics (local earthquake studies) would benefit strongly from high-sensitivity accelerometers operating at longer periods, beyond the current specifications. Long term stability of pressure sensors is of no concern for early warning applications, but is needed for geodetic applications Wet demonstrator Wet demonstrator should already return science data in addition to proving concept. In Europe a suitable location could be in Greece due to subduction related high seismicity but no large-scale cabled observatory in place. In North America Ocean Network Canada and Ocean Observatories Initiative have expressed willingness Tilmann SMART cables / Earthquakes and tsuname application 8 / 9

10 Recommendations Applications: SMART cables can significantly cut down early warning delays for tsunami early warning and improve the accuracy of forecast. A tangible improvement can also be achieved for earthquake early warning. Cable routes parallel to major subduction trenches would be of most interest to tsunami and large earthquake researchers. 50 km sensor spacing in the deep ocean would be (marginally) enough to sample details of the tsunami wavefield, allowing analysis of source and propagation effects even for non-seismic sources, such as landslides. Instrumentation: Scientific uses in global tomography and tectonics (local earthquake studies) would benefit strongly from high-sensitivity accelerometers operating at longer periods, beyond the current specifications. Long term stability of pressure sensors is of no concern for early warning applications, but is needed for geodetic applications Wet demonstrator Wet demonstrator should already return science data in addition to proving concept. In Europe a suitable location could be in Greece due to subduction related high seismicity but no large-scale cabled observatory in place. In North America Ocean Network Canada and Ocean Observatories Initiative have expressed willingness Tilmann SMART cables / Earthquakes and tsuname application 8 / 9

11 References I Tilmann SMART cables / Earthquakes and tsuname application 9 / 9